Display 'Unknown' when runner.version is empty (#24378)

Before:

![image](https://user-images.githubusercontent.com/18380374/234782197-43d8f86d-afe2-4626-8e46-b621d7cde8f9.png)
After:

![image](https://user-images.githubusercontent.com/18380374/234782064-6828ae3b-5957-451f-82bb-22ab60b6c2a8.png)

options/locale/locale_en-US.ini

@@ -109,6 +109,7 @@ error = Error
 error404 = The page you are trying to reach either <strong>does not exist</strong> or <strong>you are not authorized</strong> to view it.
 
 never = Never
+unknown = Unknown
 
 rss_feed = RSS Feed
 

templates/shared/actions/runner_list.tmpl

@@ -64,7 +64,7 @@
 						</td>
 						<td>{{.ID}}</td>
 						<td><p data-tooltip-content="{{.Description}}">{{.Name}}</p></td>
-						<td>{{.Version}}</td>
+						<td>{{if .Version}}{{.Version}}{{else}}{{$.locale.Tr "unknown"}}{{end}}</td>
 						<td>{{.OwnType}}</td>
 						<td class="runner-tags">
 							{{range .AllLabels}}<span class="ui label">{{.}}</span>{{end}}